Integrated delayed coking and thermal cracking refinery process

ABSTRACT

An integrated delayed coker and thermal cracker refinery process is provided using a single fractionator for both delayed coking and thermal cracking of a residual hydrocarbon feedstock whereby the thermal efficiency and process control of the simple integrated process are significantly improved over a comparable process producing needle or delayed coke.

nited States Patent [191 J anssen et al.

[ 51 Sept. 23, 1975 INTEGRATED DELAYED COKING AND THERMAL CRACKING REFINERY PROCESS Assignee:

Filed:

Inventors: Harry Richard Janssen; Gerald Donald Lamb, both of Ponca City, Okla.

Continental Oil Company, Ponca City, Okla.

May 2, 1973 Appl. No.: 356,540

Related US. Application Data abandoned.

Continuation of Ser. No. 150,116, June 4, 1971,

US. Cl. 208/80; 208/50; 208/67;

Int. Cl. C10B 55/00; ClOG 7/00;

Field of Search 208/80, 92, 50

References Cited UNITED STATES PATENTS GREEN 2,636,844 4/1953 Kimberlin ct a]. 208/51 2,745,794 5/1956 Alozery ct al. 208/52 2,852,439 9/1958 Jahnig ct a1 208/80 2,922.755 l/l960 Hackley 208/39 3,472,761 10/1969 Cameron 208/131 3,547,804 12/1970 Noguchi et a1. 208/46 OTHER PUBLICATIONS Kasch and Thiele Delayed Coking, A Modern Process 25 Years Old," Oil Gas Journal, pp. 89-90 (Jan. 2, 1956).

Stormont "Delayed-Coking Techniques Feel Effect of increased Needle-Coke Demand, Oil Gas Journal, pp. 75-78 (Mar. 71, 1969).

Mekler & Brooks, New Developments and Techniques in Delayed Coking, APl Div. of Refining 39 [111] pp. 229245 (May 1950).

Primary E.raminerDelbert E. Gantz Assistant Examiner-G. E. Schmitkons [57] ABSTRACT An integrated delayed coker and thermal cracker refinery process is provided using a single fractionator for both delayed coking and thermal cracking of a residual hydrocarbon feedstock whereby the thermal efficiency and process control of the simple integrated process are significantly improved over a comparable process producing needle or delayed coke.

2 Claims, 1 Drawing Figure To GAS RECOVERY 7 l T0 GAS l L" PRC RECOVERY A 2k FRC 3\ 4g 9\ COKE PRC FRC DlSTl LLATE FRC INTEGRATED DELAYED COKING AND THERMAL CRACKING REFINERY PROCESS RELATED APPLICATIONS This application is a continuation-in-part of copending application Ser. No. 150,1 16, now abandoned.

FIELD OF THE INVENTION This invention relates to a refinery process for coking and thermally cracking a residual hydrocarbon feedstock and more particularly to a process for delayed coking and thermally cracking a hydrocarbon feedstock wherein a single fractionator is used for both coking and thermal cracking.

DESCRIPTION OF THE PRIOR ART In a delayed or needle coking process, a petroleum fraction is heated under pressure to a temperature at which it will thermally decompose. The fraction is normally a residual oil or a mixture of residual oil with other fractions which are fed into a coke drum under pressure sufficient to prevent at least the heavier fractions of the oil from vaporizing until they have partially decomposed. This thermal decomposition produces a very heavy tar or pitch which undergoes additional decomposition depositing a mass of porous needle coke in the drum with the pitch.

In the typical delayed coking process, residual oil is heated by exchanging heat with liquid products from the process and is fed into a fractionating tower wherein light end products are distilled from the residual oil. The oil is then pumped from the base of the fractionating tower through a tube furnace under pressure where it is heated to the required temperature and discharged into the bottom of the coke drum where the pressure is reduced slightly. The first stages of thermal decomposition reduce this residual oil to volatile products and a very heavy tar or pitch which further decomposes to yield solid needle coke particles. The vapors formed during the decomposition produce pores and channels in the coke and pitch mass through which the incoming residual oil from the furnace must pass. The incoming oil and decomposition vapors serve to agitate and maintain the coke mass and residual oil mixture at relatively uniform temperature. This decomposition process is continued until the coke drum is filled with a mass of needle coke with a small amount of pitch. The vapors formed leave the top of the coke drum and are returned to the fractionating tower where they are fractionated into the desired petroleum cuts. After the coke drum is filled with a mixture of coke particles and some tar, the pressure is removed from the drum, residual vapors are removed, and the coke is removed from the drum by hydraulic or mechanical means. This green delayed petroleum coke has particular crystalline and chemical properties which make it especially suitable for making carbon electrodes, but the green coke must be calcined or carbonized by further treatment to produce a finished calcined coke product.

When a coker and thermal cracker are designed to produce petroleum coke, they are normally designed as two separate units. Although these units may operate simultaneously and with interconnected streams, they are completely independent and can be located either adjacent or in remote locations from each other. Typically, these units are operated primarily from storage facilities to insure a steady supply and quality of raw material for each unit. This separate operation has been considered essential for uniform operation and control although cooling and heating facilities, as well as storage facilities, are required.

In addition to the coking drums, a delayed coking unit required a separate fractionator and tube heater independent from the tube heater and fractionating unit of the thermal cracking unit, as well as a condenser and compressor for overhead products. Each of these fractionating units requires auxiliary and appurtenant equipment such as pumps, surge drums, heaters, coolers, temperature controllers, level controllers, flow controllers, and flow lines. The operation of even one of these independent units is extremely difficult since many interconnected variables are involved. In addition, the capital investment, maintenance cost, and manpower requirements for the independent units are high but have been considered essential for adequate control of the product quality, the process variables, and the raw material feedstock for each unit.

SUMMARY OF THE INVENTION It has now been discovered that a high quality product can be produced from a delayed coking unit and from a thermal cracking unit which have been integrated to utilize a single fractionator thereby practically reducing the equipment required in half. The product quality and process variable control is surprisingly easier than with the independent coking and thermal cracking units. In addition, intermediate storage can be eliminated along with heating and cooling steps. The coking unit can be either for producing a single grade, as shown in the drawing, or for producing both premium and regular grade cokes using dual sets of coking drums (which are not shown).

An integrated refinery process for delayed coking and thermal cracking hydrocarbons is provided by this invention wherein a single fractionator is utilized to serve both the delayed coking and the thermal cracking operations. The single fractionator receives the hydrocarbon residuum feedstock, fractionates it into various components which are charged separately to a thermal cracking tube heater and back into the single fractionator and through a coker tube still into the coking drums. This fractionator receives the products from both the thermal cracker tube furnace and the coking operation and fractionates both streams simultaneously for optimum yield and quality control of the desired products.

This invention provides an integrated delayed coker and thermal cracker refinery process utilizing a single fractionator and at least one set of delayed coking drums which process comprises (a) charging a liquid hydrocarbon residuum feedstock or a residuum feedstock mixed with another hydrocarbon fraction to a single fractionator, (b) fractionating said feedstock to obtain a liquid coker feedstock and a thermal cracker feedstock, (c) withdrawing said liquid coker feedstock from the bottom of said single fractionator and charging said coker feedstock to a coker heater, (d) passing said feedstock from the coker heater to a coke drum where either regular or premium needle coke forms and is deposited within said drum, (e) withdrawing the overhead product from said coke drum and returning said overhead product to said single fractionator, (f) withdrawing said thermal cracker feedstock of Step (b) from an intermediate portion of said single fractionator and charging said feedstock to a thermal cracking heater where 'said feedstock is thermally cracked, (g) returning the cracked product from the thermal cracker heater to said single fractionator, (h) withdrawing the desired hydrocarbon products from said single fractionator, and (i) recovering needle coke from said coke drum.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE shows a refinery process flow scheme utilizing a single fractionator for dual functions with a delayed coking unit and a thermal cracking tube heater.

In the FIGURE, a single fractionator l is shown having input and output distribution lines for charging and removing various hydrocarbon products to and from the fractionator. Hydrocarbon feedstock is charged to a lower portion of said fractionator l, and the feedstock is fractionated into various hydrocarbon cuts according to gravity and boiling point. Coker feedstock is withdrawn from the bottom portion of said fractionator 1 by a coker heater charge pump 15 and charged to a coker tube heater 3 where the feedstock is heated under pressure to the desired temperature. The coker feedstock is heated as it passes through the coker heater 3 and discharged into one of several delayed coking drums, either coke drum 5 or coke drum 7, where the hydrocarbon feedstock decomposes leaving a mass of needle coke suspended in thermal tar or pitch. After sufficient coke is deposited in one coke drum, the flow of the coker heater feedstock is switched to another coke drum and the coke in the first coke drum is removed. Overhead products from the coke drum 5 or coke drum 7 pass to said single fractionator l at an intermediate point on said fractionator. Thermal cracker feedstock is withdrawn from said single fractionator 1 at an intermediate point about midway of said single fractionator and said thermal cracker feedstock passes through a thermal cracker heater charge pump 17 to a thermal cracker tube furnace heater 9 where it is cracked and returned to said single fractionator l at a point in the lower portion of said single fractionator. Overhead hydrocarbon products from said single fractionator 1 pass through a condenser drum 13 A portion of said overhead products is liquified and returned to said single fractionator as liquid product which is pumped from drum 13 to an upper portion of said single fractionator 1 by a naphtha pump 21 to serve as reflux for said single fractionator. Another portion of said overhead products are withdrawn from said drum 13 and are compressed by a gas compressor 11 to the necessary pressure and sent to a gas recovery unit (not shown). An inner reflux pump 19 provides additional reflux for said single fractionator 1.

Many different types of hydrocarbon feedstocks are suitable for this integrated process, but a preferred feedstock is a residuum hydrocarbon or a mixture of residuum hydrocarbon and up to about 30 percent by weight of another hydrocarbon fraction. A typical hydrocarbon feedstock for this unit is an atmospheric or vacuum reduced virgin residuum crude. A suitable feedstock passing from the single fractionator to the coker heater is a mixture of virgin residuum and thermal tar. Hydrocarbon fractions such as gas oil or naphtha can be mixed with residuum or tar components for coker feedstock. A typical feedstock passing from the fractionator to the thermal cracking heater is a heavy gas oil. 7

When a coker and thermal cracker are designed to produce petroleum coke, they are conventionally designed as separate or independent units which may be adjacent or remotely located from each other. By combining the functions of two fractionators into a single fractionator serving a delayed coking operation and a thermal cracking operation, the units are integrated into one process which has surprising advantages and eliminates difficulties caused by features which were considered essential to previous coking and thermal cracking units. The integrated process results in surprisingly good control over the process variables for both delayed coking and thermal cracking operations, although almost half of the auxiliary equipment, namely a fractionator and associated pumps, controls, piping, and other equipment, have been eliminated. The integrated process also results in lower capital investment costs, as well as less manpower requirements to operate the unit. The integrated process of this invention permits optimization of yield as well as product quality for each hydrocarbon product, although the quantity and quality of the hydrocarbon feedstock to the integrated unit may vary with time. By combining the feedstock to each of the coking and thermal cracking units with various other hydrocarbon fractions, the quality of each unit may be maintained essentially constant, although the quality of either unit fed by the same hydrocarbon feedstock alone would fluctuate erratically. produce The flow diagram shows a simplified flow diagram for a preferred integrated delayed coking and thermal cracking operation of this invention. In the drawing, the thermal cracker is a single, heavy duty tube coil cracker producing a distillate hydrocarbon sidestream I product to the single fractionator which is also used in combination with the delayed coking operation. If distillate is not a desired product, a light oil tube coil can be added to crack the distillate into the desired lighter fractions or the distillate can be recirculated through the thermal cracker to obtain the desired product distribution. The main advantages of the integrated single fractionator delayed coking thermal cracking unit are (a) substantial savings in capital investment, (b) reduced operating manpower requirements, (0) reduced maintenance, ((1) simplified operation, piping, and unit control, and (e) optimization of quantity and quality of the desired products using a fluctuating hydrocarbon feedstock. With operating conditions and feedstock which produce a large portion of gas, there will be an increased cost in compressing this gas for other uses such as processing by gas recovery units. The thermal cracker furnace charge temperature will be slightly lower than in a separate thermal cracking unit due to lower fractionator pressure normally used with the coker cracker integrated unit. The operation and control of the single fractionator integrated unit is greatlysimplified both by elimination of unnecessary equipment as compared to the separate independent unit design and by the offsetting effect of interrelated functions. By combining the coking operation and the thermal cracking operation, many of the variables which must be precisely controlled in the independent or separate coking and cracking units are controlled internally by the various functions themselves. Therefore, there is much less chance of operator error or unit malfunction with this integrated unit. The start-up of the integrated unit is also greatly simplified over the independent unit design.

Having thus described the invention by providing specific embodiments thereof, it is understood that no undue limitations or restrictions are to be drawn by reason thereof and that many modifications and variations are within the scope of the invention, as will be recognized by those skilled in the art in view of this disclosure.

We claim:

1. An integrated refinery process including a delayed coking operation and a thermal cracking operation in which said delayed coking operation and said thermal cracking operation utilize a single fractionator, said process comprising:

a. charging a liquid hydrocarbon feedstock to a fractionator;

b. withdrawing coker feedstock from the lower portion of said fractionator and charging said coker feedstock to a coker furnace heater;

c. passing said coker feedstock from the coker furnace heater to a delayed coking drum;

(1. withdrawing overhead product from said delayed coking drum and returning said overhead product to said fractionator;

e. withdrawing thermal cracker feedstock from an intermediate portion of said fractionator and charging saidthermal cracker feedstock to a thermal cracking furnace;

f. thermally cracking said thermal cracker feedstock in said thermal cracking furnace and returning the cracked material to said fractionator;

g. operating said fractionator receiving said liquid hydrocarbon feedstock, said overhead product from the delayed coking drum and said cracked material to produce coker feedstock and thermal cracker feedstock; and

h. recovering delayed coke from said delayed coking drum.

2. The process of claim 1 wherein the feedstock charged to said fractionator is an atmospheric or vacuum virgin residuum. 

1. AN INTEGRATED REFINERY PROCESS INCLUDING A DELAYED COKING OPERATION AND A THERMAL CRACKING OPERATION IN WHICH SAID DELAYED COKING OPERATION AND SAID THERMAL CRACKING OPERATION UTILIZE A SINGLE FRACTIONATOR, SAID PROCESS COMPRISING: A. CHARGING A LIQUID HYDROCARBON FEEDSTOCK TO A FRACTIONATOR, B. WITHDRAWING COKER FEEDSTOCK FROM THE LOWER PORTION OF SAID FRACTIONATOR AND CHARGING SAID COKER FEEDSTOCK TO A COKER FUNANCE HEATER, C. PASSING SAID COKER FEEDSTOCK FROM THE COKER FURNACE HEATER TO A DELAYED COKING DRUM, D. WITHDRAWING OVERHEAD PRODUCT FROM SAID DELAYED COKING DRUM AND RETURNING SAID OVERHEAD PRODUCT TO SAID FRACTIONATOR,
 2. The process of claim 1 wherein the feedstock charged to said fractionator is an atmospheric or vacuum virgin residuum. 